Lumbar support assemblies are used for maintaining a seat cushion in a contoured position. Such lumbar support assemblies usually include either bellows or air bladders and a pump to force air into the cushion pocket until a desired contour is reached. A semi-rigid mechanical structure, which can be moved in a plurality of predetermined positions to adjust the contour of the seat in the lumbar area, is also known.
U.S. Pat. No. 5,076,643, issued Dec. 31, 1991 in the name of Colasanti et al, and assigned to the assignee of the subject invention, discloses a lumbar support assembly having a seat frame with a pneumatic bladder supported thereon. A contoured plate is disposed over the bladder having a free end slidably engaged with guides. As the bladder is inflated and deflated, the plate responds thereto providing lumbar support as required.
U.S. Pat. No. 5,137,329, issued Aug. 11, 1992 in the name of Neale discloses a lumbar support mechanism having an actuator located behind a rigid plate. An upper chamber and a lower chamber are located within the actuator. The chambers are expandable and inflate independently of each other. As the actuator inflates either or both of the chambers, the plate moves to provide the desired lumbar support.
U.S. Pat. No. 5,082,326, issued Jan. 21, 1992 in the name of Sekido et al discloses a vehicle seat having a number of inflatable bladders used for comfort control adjustment. A clam-shell shaped air bladder is disclosed. Furthermore, U.S. Pat. No. 3,326,601, issued Jun. 20, 1967 in the name of Vanderbilt et al discloses the use of a clam-shaped air bladder.
A problem with the prior art is that such air bladders tend to cause uneven distribution of air pressure in the lumbar area, i.e., the bags tend to bow in the center providing uneven support of the plate.